Life Below Zero

by Gretchen Noyes-Hull

Moving through the deep snows of the highest mountains and the tangled tunnels of sea ice, or waiting deep inside the ice of permafrost, ancient glaciers, and polar lakes, small organisms carry on their secret lives!

On a snapshot of Earth from space, the tremendous expanses of frozen whiteness stand out frigid and lifeless. But not so quick! Scientists everywhere are bundling off to the coldest corners of the Earth to study small organisms found there, thriving at temperatures well below the freezing point of water. The pace of the researchers' efforts has quickened now, for these scientists also know that their results will guide the search for life in other icy realms of our solar system.

Creatures that live inside the ice and snow live on the very edge of possibilities! Surrounding ice crystals close in like piercing daggers as the fragile cells fight to keep from freezing solid. Some microbes simply enclose themselves with strong walls and wait inside for warmer times. Most manufacture substances to serve as “antifreeze” in preventing the formation of ice crystals within their cells. Some secrete forms of slime to melt the ice immediately around them, and others find living arrangements where the ice never freezes.

The discovery of ancient living cells within the ice has given new meaning to the expression “frozen in time.” From permafrost and ancient glacier ice, organisms have been coaxed back to life. Moss once entombed in the Siberian permafrost for 40,000 years now grows quite happily in laboratory cultures. From all over the world, bacteria locked for thousands of years deep inside glaciers have been awakened from their dormancy.

Beautiful marine diatoms (one-celled algae with silica exoskeletons) such as these seen through a microscope multiply in cold ocean water after the ice breaks up.

By far the oldest of these or any live organisms yet discovered are the bacteria that have been retrieved from almost 4 kilometers (2.5 miles) deep in Antarctic glacier ice. These cells had last seen the cold light of day between 500,000 and a million years ago! Throughout their slow drift downward in the ice, they had remained in a sort of suspended animation. Now back at the surface once more, they may answer many questions we have about long-term survival below, on their own and other planets.

The more modern cousins of these ancient cells may also give us some clues. Every year, bacteria are carried on the wind to the frozen surfaces of Antarctic lakes. These hardy microbes continue to grow throughout the dark, subzero winters by clinging to “life rafts” of dirt and dust particles. The particles give off just enough heat to slowly melt their way down into the ice as they provide nutrients and tiny envelopes of liquid water to the bacteria that cling to them.

Each winter, the return of the sea ice to the polar oceans re-creates a magical kingdom of interconnecting tunnels and passages for communities of cold-loving creatures. When ocean water freezes, it leaves the salt behind. The result is freshwater ice interlaced with channels of a highly concentrated salt solution called “brine.” Even at temperatures well below zero degrees Celsius, brine remains fluid and keeps open the tiny ice passageways within the ice. The bacteria, algae, and animals that all seek shelter and liquid water inside the icy network often turn the sea ice brown with their pigments.

The entire food web of the polar oceans depends on the annual formation of sea ice. Each winter, the ice shelters a vast population of growing algae and a nursery of developing larvae. Each spring, when the waters warm, the sea ice breaks apart and releases algae cells and tiny animals back to the sea. There they continue to grow and become food for the larger animals. In the Antarctic Ocean, crustaceans known as krill voraciously graze first on the curtains of algae that protrude from the sea ice and then on the small diatom cells that multiply in the cold ocean water when the ice breaks up. A photograph taken from space shows 13 percent of the Earth's surface to be glazed with sea ice. It reveals nothing of the briny inhabitants within!

These exotic-looking microbes turned up in Antarctic ice from as deep as 1,249 meters. The researchers who first saw them gave them fanciful names such as Mickey Mouse (right) and Klingon (center), based on passing resemblances.

“Watermelon snow” sounds like a new flavor of soft-serve! Although those who have tried it say it isn't too tasty, it does provide visible evidence of another “below zero” community. Especially in the high mountains where the snow is lasting, and wherever it is deep, its ice crystals provide passageways that other organisms use to find shelter and food. The algae that turn the snow red, or sometimes pink and orange, spend most of their lives sealed off from the cold and the prickly crystals in their walled cysts deep beneath the snow.

When the spring sun melts the top layers of the snow, water percolates down to announce the warm weather above. The cysts split open, releasing “flagellated” algae. The flagella are whip-like appendages that propel the cells rapidly upstream to the snow surface. During their brief time in the sun, the cells grow and reproduce, using their brightly colored pigments as sunscreen to protect them from the ultraviolet light that glares off the snow. When snow flies again, the cells form cysts once more and sink beneath its cold white blanket.

Snow algae are not alone in their icy-cold world. A whole range of animals that wriggle between the snow crystals apparently do find them tasty. The most famous is the “ice worm,” a tiny cousin of the earthworm so acclimated to the cold that it dies if the temperature goes much above zero degrees Celsius. During the day it seeks shelter 1.8 meters (six feet) under the snow, rejoining its friends only at night. When temperatures fall again, they form a carpet of short black threads on the surface of the snow.

So, let's remember to step just a little more lightly the next time we go tromping around on the white stuff. By doing so, we can show our respect for those tiny creatures who have adapted so well to life below zero.

Ice by Any Other Name

by Gretchen Noyes-Hull

Frazil, grease, shuga, pancake, floe, pack, first year, multiyear, and fast ice are just a few of the words for the ice of the polar seas. The names follow the stages of its formation as the temperature drops each winter.

Ocean water does not even begin to freeze until its surface temperature dips below minus 1.89 degrees C (28 degrees F). Microscopic disc-shaped crystals then begin to form and quickly grow. Still less than a millimeter long, the crystals, known as “frazil,” rise to the surface and congeal. Small organisms may become trapped within the gathering crystals.

Because of its appearance, the skim coating is known as “grease ice,” or “shuga” when it collects in spongy white lumps similar to confectioner's sugar. Stirred by the wave action and cemented by decreasing temperatures, the chunks start to collect in large, pancake-shaped floes often 2.5 meters (8 feet) in diameter. Pushing and shoving into each other, the “pancakes” begin to freeze together in rough sheets. As the temperature continues to fall, the sea ice thickens and crowds together as “pack ice.” Pack ice that survives the spring melt for another season of cold is called “multiyear ice.” “Fast” ice does not move as its name implies, but is held fast to the land.

Space Ice

by Gretchen Noyes-Hull

There is plenty of ice out there! We have recently detected crystals of ice hidden in shaded polar craters of the moon and a deep permafrost and liquid ice on the surface of Mars. A rind of solid ice that encases Jupiter's moon, Europa, could hide a liquid ocean from our view.

Until the last few years, the mention of possible life, past or present, on other planets would have produced raised eyebrows and a bemused smile. The simultaneous discovery of organisms that survive apparently indefinitely in Earth-bound ice and of ice elsewhere in the solar system has changed all that. The intense conversation between polar research scientists and astrobiologists, who focus on the search for extraterrestrial life, reflects the excitement.

In particular, it is the bacteria found in deep Antarctica glacial ice that have stirred the scientific world. Russian and American researchers have drilled their cores 4 kilometers (2.5 miles) below the surface, stopping just short of what appears to be an enormous ancient lake sealed off from the atmosphere millions of years ago. Lake Vostok itself has not yet been sampled, for fear of contaminating it with modern-day organisms, but the ice directly above it harbors living bacteria trapped in the cold a very long time ago.

Scientists are now pooling their efforts to design methods to safely sample the lake. They know that these same techniques may be used to sample deep under the icy surface of Europa in the not-so-distant future, or to retrieve samples from icy Martian or lunar soils.

No more raised eyebrows! There is a distinct possibility that life will be found in distant ice-bound worlds.

Vocabulary

algae:

Any of a large group of simple living things that grow in water.

appendage:

A part of the body that comes out from another part.

bacteria:

Tiny one-celled organisms.

crustaceans:

Any of a group of arthropods that live mostly in water and have a hard outer covering. Lobsters, crabs, and shrimp are crustaceans.

culture:

The growing of living cells or microscopic organisms in a laboratory.

frigid:

Extremely cold.

microbe:

A very tiny living organism.

nutrient:

A substance that living things need in order to survive and grow.

percolate:

To be lively or active.

permafrost:

Permanently frozen subsoil, occurring throughout the polar regions and other regions that remain permanently cold.